Boron dipyrromethene dyes attract steadily growing interest as therapeutic and diagnostic tools. Therefore, their ground-state vibrational spectra deserve special attention. Resonance Raman spectroscopy can be advantageously exploited to rationally understand the vibrational properties of molecular chromophores. Interference from fluorescence should be avoided if detailed measurements are to be performed. We have obtained resonance Raman spectra of a model molecule for boron dipyrromethene dyes through a judicious choice of the sample and the measurement conditions. These included spectra at the solid state and surface-enhanced spectra on dispersed silver nanoparticles. The results can form the basis for the interpretation of the spectral features of related dyes bearing complex chemical substituents.

Boron dipyrromethene (BODIPY) derivatives are an important class of organic molecular dyes. Their chemical structure can be easily modified by synthetic methods, introducing various substituent groups on a tricyclic core that represents the characteristic unit of these compounds. As a consequence, BODIPY optical properties can be designed to tune their absorption and emission in an especially wide wavelength range. A large amount of experimental and computational studies has been performed to investigate the electronic excited states of many structurally different BODIPY dyes. On the other hand, vibrational properties are by far less known for these compounds. We have therefore measured detailed infrared and Raman spectra of a model compound, namely, a BODIPY derivative with four methyl groups and a phenyl ring as substituents. The experimental spectra of the solid sample have been contrasted with ab initio spectra computed at the CAM-B3LYP/6-31G+(d) +(d) level. Computations have been performed both for the isolated molecule and including the crystalline environment. In the latter case, better agreement has been observed. An assignment is proposed for the 123 vibrational modes. These results form the basis for further spectroscopic studies on complex BODIPY derivatives.

An experimental study on an innovative contrast agent is presented. This work demonstrates that copper sulfide in the form of small-sized nanoparticles can be exploited in photoacoustic imaging. An advantage of this material is strong light absorption in the near-infrared range, especially in the transparency windows of biological tissues. In order to yield a proper contrast, light absorption must be followed by heat release with high efficiency. Therefore, it is important to evaluate the photochemical conversion efficiency of the material. We applied a method that is strictly related to photoacoustic applications. The nanoparticles were produced according to a well-established synthesis. Subsequently, they were diluted in pure water to obtain an extinction <0.2/cm at 1064 nm. The photoacoustic signals, generated by 1064 nm laser excitation, were analyzed as a function of concentration and incident laser energy below 70 μJ /pulse. The signals were carefully compared with those of a reference aqueous solution, containing a light-absorbing ionic solute. Data analysis yielded a light-to-heat conversion efficiency 1.0 (±0.1). We discuss this result by comparison with related studies on other types of copper sulfide nanoparticles, where the conversion efficiency reportedly varied from 33% to 93%. The high value determined in the present study possibly indicates that resonant light scattering and luminescence are negligible for our material system.

Vibrational spectroscopy methods display great potential in the study of biomolecules. The complexity of these molecular systems, though, is often a hindrance for the interpretation of the experimental spectra. Selective techniques should therefore be improved and applied extensively. This article presents surface enhanced Raman spectra of an important model protein, namely, wheat germ agglutinin. To obtain these spectra, a novel substrate for the protein has been developed. The substrate is based on gold nanospheroids, produced by wet synthesis. The nanoparticles are then functionalized by reaction with a solution of β-D-thioglucose to increase the affinity of the agglutinin for the surface. When nanoparticle films are placed in contact with diluted agglutinin solutions, vibrational bands of the protein appear and can be easily discriminated from those of the substrate. The Raman bands of the substrate and of the protein have then been assigned correlatively. On this basis, we conclude that the interaction between the agglutinin and the nanoparticles is selectively detected only when the metal surface is suitably functionalized.

Plasmonic systems are becoming a favourable alternative to dye molecules in the generation of photoacoustic signals for spectroscopy and imaging. In particular, inorganic nanoparticles are appealing because of their versatility. In fact, as the shape, size and chemical composition of nanoparticles are directly correlated with their plasmonic properties, the excitation wavelength can be tuned to their plasmon resonance by adjusting such traits. This feature enables an extensive spectral range to be covered. In addition, surface chemical modifications can be performed to provide the nanoparticles with designed functionalities, e.g., selective affinity for specific macromolecules. The efficiency of the conversion of absorbed photon energy into heat, which is the physical basis of the photoacoustic signal, can be accurately determined by photoacoustic methods. This review contrasts studies that evaluate photoconversion in various kinds of nanomaterials by different methods, with the objective of facilitating the researchers' choice of suitable plasmonic nanoparticles for photoacoustic applications.

Glyphosate is a wide spread organophosphate herbicide whose use and associated risks are strongly debated. Many countries are regulating its use in field and it is often found in surface water. Therefore, a simple analytical method, possibly based on portable instruments, would be highly desirable. In case of many other pesticides, surface enhanced Raman scattering (SERS) spectroscopy was shown to be a very effective method to approach the problem. Glyphosate Raman and SERS spectra have been subject of different experimental and theoretical studies but still their interpretation is unclear and sensitivity in SERS experiments is quite low. In this work, SERS spectra on silver nanoparticles dispersion of glyphosate, its 2-13C isotopically substituted derivative, and its degradation product, the aminomethylphosphonic acid, have been obtained. The vibrational spectra of this latter compound allowed us to rule out a possible contribution of this species to the SERS spectra and the observed isotope shifts help to explain the SERS pattern in terms of the orientation of the adsorbed molecules on the metal surface. Therefore, we conclude that the relevant differences both on the intensities and wavenumbers between our SERS and Raman spectra of glyphosate must derive from the effect induced by the adsorption on the nanoparticles.

Dimethoate (DMT) is an organophosphate insecticide commonly used to protect fruit trees and in particular olive trees. Since it is highly water-soluble, its use on olive trees is considered quite safe, because it flows away in the residual water during the oil extraction process. However, its use is strictly regulated, specially on organic cultures. The organic production chain certification is not trivial, since DMT rapidly degrades to omethoate (OMT) and both disappear in about two months. Therefore, simple, sensitive, cost-effective and accurate methods for the determination of dimethoate, possibly suitable for in-field application, can be of great interest. In this work, a quick screening method, possibly useful for organic cultures certification will be presented. DMT and OMT in water and on olive leaves have been detected by surface enhanced Raman spectroscopy (SERS) using portable instrumentations. On leaves, the SERS signals were measured with a reasonably good S/N ratio, allowing us to detect DMT at a concentration up to two orders of magnitude lower than the one usually recommended for in-field treatments. Moreover, detailed information on the DMT distribution on the leaves has been obtained by Raman line- (or area-) scanning experiments.

Self-association of proteins forming dimers or oligomers is a common occurrence in biological systems. Probing the dimerization status can be performed by various size- and mass-selective methods (e.g. analytical ultracentrifugation, gel filtration, ċċċ). Every method has its strengths but generally the detection directly in the solution by optical means is preferred. Metal nanoparticles (NP) can be observed in a light microscope and their surface can be functionalized with different chemical compounds, like dyes or affinity tags. For example, nickel-chelated N-nitrilo-triacetic acid (Ni-NTA) functionalized metal nanoparticles (Ni-NTA NP) can be site-specifically attached to His-tagged proteins, forming a thin single protein layer on a NP. Additional functionalization of the Ni-NTA NP with Raman or fluorescent dyes provide furthermore the ability to observe red-shifted emissions, like surface-enhanced Raman scattering (SERS) or surface-enhanced fluorescence (SEF), especially if plasmonic metals are used as NP material. Those effects are large if single NPs are near to each other upon laser irradiation. In case the NP surface attached proteins form stable dimers or oligomers, the functionalized NPs will be concomitantly linked and in close proximity to each other, forming NP dimers or oligomers itself. The new formed NP-complexes can be detected by dynamic light scattering (DLS), asymmetric flow field fractionation (AFFF) or observed optically on the single-particle level by red-shifted emissions upon laser irradiation. Observing the red-shifted emissions, inelastic scattering (Raman/Mie) or fluorescence, concomitantly with elastic (Rayleigh) emissions via two separate imaging channels in a light-sheet illumination approach allows the check of the NP-dimerization/oligomerization status. This indicates protein interaction in the native suspension environment and enables determination of the ratio of non-oligomerized to oligomerized protein in a microscope image or video. This approach paves the way for fast optical determination of protein-protein or protein-ligand interactions.

We report here on the efficient and straightforward synthesis of a series of modular and functional PBA-BODIPY dyes 1-4. They are an outstanding example of the efficient merge of the versatility of the 3,5-dichloro-BODIPY derivatives and the receptor-like ability of the PBA moiety. The potential bioanalytical applicability of these tools was assessed by measuring the binding to glycan chains of antibodies by a Quartz Crystal Microbalance (QCM).

The triplatinum complex of the 2,4,6-Tris(2-pyrimidyl)-1,3,5-triazine ligand, Pt(3)TPymT hereafter, has been prepared and characterized for the first time. NMR studies point out that the three platinum(II) centers possess an identical coordination environment. The interactions of Pt(3)TPymT with DNA were explored in comparison to the free ligand. Specifically, fluorescence, mass spectrometry, viscometry and melting measurements were carried out. In contrast to expectations, the obtained data reveal that no intercalative binding takes place; we propose that binding of Pt(3)TPymT to DNA mainly occurs through external/groove binding.

The ligand binding characteristics of heme-containing proteins are determined by a number of factors, including the nature and conformation of the distal residues and their capability to stabilize the heme-bound ligand via hydrogen-bonding and electrostatic interactions. In this regard, the heme pockets of truncated hemoglobins (TrHbs) constitute an interesting case study as they share many common features, including a number of polar cavity residues. In this review, we will focus on three proteins of group II TrHbs, from Thermobifida fusca (Tf-HbO) and Pseudoalteromonas haloplanktis TAC125 (Ph-HbO). Although the residues in positions G8 (Trp) and B10 (Tyr) are conserved in all three proteins, the CD1 residue is a Tyr in T. fusca and a His in P. haloplanktis. Comparison of the ligand binding characteristics of these proteins, in particular the hydroxo and CO ligands by means of resonance Raman spectroscopy, reveals that this single difference in the key heme cavity residues markedly affects their ligand binding capability and conformation. Furthermore, although the two Ph-HbOs (Ph-HbO-2217 and Ph-HbO-0030) have identical key cavity residues, they display distinct ligand binding properties.

Surface-enhanced Raman scattering (SERS) is increasing in significance as a bioanalytical tool. Novel nanostructured metal substrates are required to improve performances and versatility of SERS spectroscopy. In particular, as biological tissues are relatively transparent in the infrared wavelength range, SERS-active materials suitable for infrared laser excitation are needed. Nanowires appear interesting in this respect as they show a very broad localized surface plasmon resonance band, ranging from near UV to near infrared wavelengths. The SERS activity of silver nanowires has been tested at three wavelengths and a fair enhancement at 1064 and 514 nm has been observed, whereas a very weak enhancement was present when exciting close to the nanowire extinction maximum. These experimentally measured optical properties have been contrasted with finite element method simulations. Furthermore, laser-induced optoacoustic spectroscopy measurements have shown that the extinction at 1064 nm is completely due to scattering. This result has an important implication that no heating occurs when silver nanowires are utilized as SERS-active substrates, thereby preventing possible thermal damage.

Doubly functionalized, hierarchical-porosity silica monoliths were synthesized by postgrafting of sulfonic groups and in situ growth of Pd nanoparticles in that order. PdNP of 3.1 nm size located in the mesopores of the material showed to be evenly distributed within 4.6% wt Pd monoliths. The system was explored in the continuous-flow, catalytic partial hydrogenation reaction of 3-halogeno-nitrobenzenes and 3-hexyn-1-ol in the liquid phase, showing remarkable conversion, selectivity, and resistance under very mild conditions.

The use of nanoparticles for many advanced applications (drug-delivery, biosensors, catalysts etc.) involves their large scale production. This engenders the need of synthetic methods and reactants which are sustainable as well as safe. Natural products allow to prepare nanoparticles via eco-friendly processes, which is especially true for reducing/capping agents obtained from agricultural by-products. Here, we prepared gold nanoparticles (AuNPs) in high yields by using extracts from the leaves of marketable plants and by following different synthetic routes (i.e. one- or two-steps). The size and morphology of the obtained AuNPs were determined by Transmission Electron Microscopy (TEM), while surface coverage with different chemical species was investigated by surface-enhanced Raman scattering (SERS). In vitro experiments on bone-marrow mesenchymal stromal cells (MSCs) were used to study the effect on cell viability, as a first step toward toxicity assessment. This work allowed to select the nanoparticles with highest SERS activity at infrared excitation wavelength, in view of their possible use as shelf products.

An inverse (water in oil) miniemulsion technique was successfully implemented for the first time for the synthesis of crystalline pure and doped CuS nanostructures for applications in photothermal therapy. Different copper and sulfur sources were tested for the preparation of the targeted compounds. The successful formation at room temperature of the covellite crystalline phase was determined by means of X‐ray diffraction crystallography, selected‐area electron diffraction, and X‐ray absorption spectroscopy. The morphology of the nanostructures was assessed by scanning and transmission electron microscopy, while the surface composition was determined by X‐ray photoelectron spectroscopy. Further investigations, aimed at obtaining a characterization as detailed as possible, were performed by combining the outcomes of complementary techniques. Droplet‐size variations, as a function of sonication time and/or mode, were studied using dynamic light‐scattering measurements. A high microscopic photothermal conversion efficiency – a relevant property for photothermal therapy and photoacoustic imaging – was determined by calibrated optoacoustic measurements. The photothermal efficiency of diluted aqueous dispersions of the CuS nanostructures is ≥ 0.72, as determined by laser excitation at 1064 nm.

An assay for Survivin, a small dimeric protein which functions as modulator of apoptosis and cell division and serves as a promising diagnostic biomarker for different types of cancer, is presented. The assay is based on switching on surface-enhanced Raman scattering (SERS) upon incubation of the Survivin protein dimer with Raman reporter-labeled gold nanoparticles (AuNP). Site-specificity is achieved by complexation of nickel-chelated N-nitrilo-triacetic acid (Ni-NTA) anchors on the particle surface by multiple histidines (His6 -tag) attached to each C-terminus of the centrosymmetric protein dimer. Correlative single-particle analysis using light sheet laser microscopy enables the simultaneous observation of both elastic and inelastic light scattering from the same sample volume. Thereby, the SERS-inactive AuNP-protein monomers can be directly discriminated from the SERS-active AuNP-protein dimers/oligomers. This information, i.e. the percentage of SERS-active AuNP in colloidal suspension, is not accessible from conventional SERS experiments due to ensemble averaging. The presented correlative single-particle approach paves the way for quantitative site-specific SERS assays in which site-specific protein recognition by small chemical and in particular supramolecular ligands can be tested.

An assay for protein dimers using surface-enhanced Raman scattering (SERS) is presented, in article number 1700802, by Sebastian Schlücker and co-workers. Site-specific binding of the Survivin protein dimer to molecularly functionalized gold nanoparticles results in the formation of protein-bridged dimers of gold nanoparticles. The dimers exhibit the characteristic SERS spectrum of Raman reporter molecules in the hot spot generated upon resonant laser excitation.

An optofluidic light detector based on the photoacoustic effect is presented. The device performances are tested at 532nm using a pulsed solid-state laser as light source and a potassium permanganate (KMnO4) water solution as active medium. As expected, the device shows linear response with respect to applied light irradiance. By changing flow rate the device sensitivity increases non-linearly. This change in sensitivity is mainly attributed to a rise in water temperature as the flow rate increases, leading to a higher thermal expansion coefficient. Changes of water temperature with applied flow rate are confirmed through independent fluorescence intensity experiments with Rhodamine B in water. Comparison of the photoacoustic and fluorescence data points out that the change in temperature inside the microfluidic device is not promoted by the absorbed laser light, but instead is mainly due to viscous friction.

We contrast recently reported surface-enhanced resonance Raman spectra (SERRS) of myoglobin on silver nanoparticles with established knowledge about this complex. We conclude that the detected bands are not related to the spin states of the protein cofactor, being rather originated by a heme coordination change induced by the metal surface.